Principles of anatomy and physiology 13th ed g tortora, b derrickson (wiley, 2011) 1

JWCL316_fm_i-xxxiv.qxd 17/11/2010 21:22 Page i Principles of ANATOMY & PHYSIOLOGY 13th Edition Gerard J Tortora Bergen Community College Bryan Derrickson Valencia Community College John Wiley & Sons, Inc JWCL316_fm_i-xxxiv.qxd 11/22/10 7:01 PM Page ii Vice President & Publisher Executive Editor Executive Marketing Manager Developmental Editor Senior Media Editor Project Editor Program Assistant Production Manager Production Editor Senior Illustration Editor Illustration Coordinator Senior Designer Text Designer Photo Department Manager Production Management Services Kaye Pace Bonnie Roesch Clay Stone Mary Berry Linda Muriello Lorraina Raccuia Lauren Morris Dorothy Sinclair Sandra Dumas Anna Melhorn Claudia Volano Madelyn Lesure Brian Salisbury Hilary Newman Ingrao Associates Page layout was completed by Laura Ierardi, LCI Design Photo Credits Front cover photo credits (bottom left to right): (muscle) ©Mark Nielsen; (neuron cell body) ©Dr Don Fawcett/Visuals Unlimited/Getty Images, Inc.; (ear cross-section) ©MedicalRF.com/Getty Images, Inc.; (red blood cells) ©Dr Don Fawcett/Visuals Unlimited/Getty Images, Inc.; (spinal cord) ©Ron Boardman/Stone/Getty Images, Inc Back cover photo credits: (top left) ©Dr Don Fawcett/Visuals Unlimited/Getty Images, Inc.; (top right) ©Ron Boardman/Stone/Getty Images, Inc.; (center left) ©Mark Nielsen; (center right) ©Dr Don Fawcett/Visuals Unlimited/Getty Images, Inc.; (bottom) ©MedicalRF.com/Getty Images, Inc This book was typeset in 10.5/12.5 Times at Aptara®, Inc and printed and bound by Quad Graphics The cover was printed by Quad Graphics Founded in 1807, John Wiley & Sons, Inc., has been a valued source of knowledge and understanding for more than 200 years, helping people around the world meet their needs and fulfill their aspirations Our company is built on a foundation of principles that include responsibility to the communities we serve and where we live and work In 2008, we launched a Corporate Citizenship Initiative, a global effort to address the environmental, social, economic, and ethical challenges we face in our business Among the issues we are addressing are carbon impact, paper specifications and procurement, ethical conduct within our business and among our vendors, and community and charitable support For more information, please visit our website: www.wiley.com/go/citizenship The paper in this book was manufactured by a mill whose forest management programs include sustained yield harvesting of its timberlands Sustained yield harvesting principles ensure that the number of trees cut each year does not exceed the amount of new growth This book is printed on acid-free paper Copyright © 2012, 2009, 2006, 2003, 2000 © Biological Science Textbooks, Inc., and Bryan Derrickson No part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means, electronic, mechanical, photocopying, recording, scanning or otherwise, except as permitted under Sections 107 or 108 of the 1976 United States Copyright Act, without either the prior written permission of the Publisher or authorization through payment of the appropriate per-copy fee to the Copyright Clearance Center, 222 Rosewood Drive, Danvers, MA 01923, (978) 750-8400, fax (978) 646-8600 Requests to the Publisher for permission should be addressed to the Permissions Department, John Wiley & Sons, Inc., 111 River Street, Hoboken, NJ 07030-5774, (201) 748-6011, fax (201) 748-6008 Evaluation copies are provided to qualified academics and professionals for review purposes only, for use in their courses during the next academic year These copies are licensed and may not be sold or transferred to a third party Upon completion of the review period, please return the evaluation copy to Wiley Return instructions and a free-of-charge return shipping label are available at www.wiley.com/go/returnlabel Outside of the United States, please contact your local representative ISBN 13 978-0470-56510-0 ISBN 13 978-0470-91777-0 Printed in the United States of America 10 JWCL316_fm_i-xxxiv.qxd 17/11/2010 21:22 Page iii HELPING TEACHERS AND STUDENTS SUCCEED TOGETHER An anatomy and physiology course can be the gateway to a gratifying career in a whole host of health-related professions It can also be an incredible challenge Through years of collaboration with students and instructors alike, we have come to intimately understand not only the material but also the evolving dynamics of teaching and learning A&P So with every new edition, it’s our goal to find new ways to help instructors teach more easily and effectively and students to learn in a way that sticks We believe we bring together experience and innovation like no one else, offering a unique solution for A&P designed to help instructors and students succeed together From constantly evolving animations and visualizations to design based on optimal learning to lessons firmly grounded in learning outcomes, everything is designed with the goal of helping instructors like you teach in a way that inspires confidence and resilience in students and better learning outcomes The thirteenth edition of Principles of Anatomy and Physiology, integrated with WileyPLUS, builds students’ confidence; it takes the guesswork out of studying by providing students with a clear roadmap (one that tells them what to do, how to it, and if they did it right) Students will take more initiative, so instructors can have greater impact Principles of Anatomy and Physiology 13e continues to offer a balanced presentation of content under the umbrella of our primary and unifying theme of homeostasis, supported by relevant discussions of disruptions to homeostasis In addition, years of student feedback have convinced us that readers learn anatomy and physiology more readily when they remain mindful of the relationship between structure and function As a writing team—an anatomist and a physiologist—our very different specializations offer practical advantages in fine-tuning the balance between anatomy and physiology On the following pages students will discover the tips and tools needed to make the most of their study time using the integrated text and media Instructors will gain an overview of the changes to this edition and of the resources available to create dynamic classroom experiences as well as build meaningful assessment opportunities Both students and instructors will be interested in the outstanding resources available to seamlessly link laboratory activity with lecture presentation and study time iii JWCL316_fm_i-xxxiv.qxd 17/11/2010 21:23 Page iv N OT E S TO The challenges of learning anatomy and physiology can be complex and time-consuming This textbook and WileyPLUS for Anatomy and Physiology have been carefully designed to maximize your study time by simplifying the choices you make in deciding what to study and how to study it, and in assessing your understanding of the content S T U D E N T S Anatomy and Physiology Is a Visual Science Studying the figures in this book is as important as reading the narrative The tools described here will help you understand the concepts being presented in any figure and ensure that you get the most out of the visuals LEGEND Read this first It explains what the figure is about Figure 24.11 External and internal anatomy of the stomach KEY CONCEPT STATEMENT Indicated by a “key” icon, this reveals a basic idea portrayed in the figure The four regions of the stomach are the cardia, fundus, body, and pyloric part Esophagus ORIENTATION DIAGRAM Added to many figures, this small diagram helps you understand the perspective from which you are viewing a particular piece of anatomical art FUNDUS Lower esophageal sphincter Serosa Muscularis: CARDIA BODY Longitudinal layer Lesser curvature Circular layer FIGURE QUESTION Found at the bottom of each figure and accompanied by a “question mark” icon, this serves as a self-check to help you understand the material as you go along PYLORUS Oblique layer Greater curvature FUNCTIONS BOX Included with selected figures, these provide a brief summary of the functions of the anatomical structure or system depicted Duodenum Pyloric sphincter PYLORIC CANAL Rugae of mucosa FUNCTIONS OF THE STOMACH PYLORIC ANTRUM Mixes saliva, food, and gastric juice to form chyme (a) Anterior view of regions of stomach Esophagus Serves as reservoir for food before release into small intestine Secretes gastric juice, which contains HCl (kills bacteria and denatures protein), pepsin (begins the digestion of proteins), intrinsic factor (aids absorption of vitamin B12), and gastric lipase (aids digestion of triglycerides) Figure 23.17 Changes in partial pressures of oxygen and carbon dioxide (in mmHg) during external and internal Secretes gastrin into blood respiration Gases diffuse from areas of higher partial pressure to areas of lower partial pressure Duodenum Atmospheric air: PO2 = 159 mmHg PCO = 0.3 mmHg CO2 exhaled O2 inhaled PYLORUS Pyloric sphincter PYLORIC CANAL Lesser curvature FUNDUS CARDIA Alveoli BODY CO2 O Alveolar air: PO2 = 105 mmHg PCO = 40 mmHg PYLORIC ANTRUM Rugae of mucosa Pulmonary capillaries (a) External respiration: pulmonary gas exchange Greater curvature To left atrium To lungs (b) Anterior view of internal anatomy After a very large meal, does your stomach still have rugae? Deoxygenated blood: PO2 = 40 mmHg PCO = 45 mmHg Oxygenated blood: PO = 100 mmHg PCO = 40 mmHg To right atrium MP3 DOWNLOADS In each chapter you will find that several illustrations are marked with an icon that looks like an iPod This indicates that an audio file that narrates and discusses the important elements of that particular illustration is available You can access these downloads on the student companion website or within WileyPLUS To tissue cells (b) Internal respiration: systemic gas exchange Systemic capillaries CO2 O2 Systemic tissue cells: PO2 = 40 mmHg PCO = 45 mmHg What causes oxygen to enter pulmonary capillaries from alveoli and to enter tissue cells from systemic capillaries? iv JWCL316_fm_i-xxxiv.qxd 11/22/10 7:00 PM N OT E S Page v TO S T U D E N T S Physiology of Hearing The following events are involved in hearing (Figure 17.22): ● ● Studying physiology requires an understanding of the sequence of processes Correlation of sequential processes in text and art is achieved through the use of special numbered lists in the narrative that correspond to numbered segments in the accompanying figure This approach is used extensively throughout the book to lend clarity to the flow of complex processes ● ● The auricle directs sound waves into the external auditory canal When sound waves strike the tympanic membrane, the alternating waves of high and low pressure in the air cause the tympanic membrane to vibrate back and forth The tympanic membrane vibrates slowly in response to low-frequency (low-pitched) sounds and rapidly in response to highfrequency (high-pitched) sounds The central area of the tympanic membrane connects to the malleus, which vibrates along with the tympanic membrane This vibration is transmitted from the malleus to the incus and then to the stapes As the stapes moves back and forth, its oval-shaped footplate, which is attached via a ligament to the circumference of the oval window, vibrates in the oval window The vibrations at the oval window are about 20 times more vigorous than the tympanic membrane because the auditory ossicles efficiently transmit small vibrations spread over a large surface area (the ● ● ● ● ● tympanic membrane) into larger vibrations at a smaller surface (the oval window) The movement of the stapes at the oval window sets up fluid pressure waves in the perilymph of the cochlea As the oval window bulges inward, it pushes on the perilymph of the scala vestibuli Pressure waves are transmitted from the scala vestibuli to the scala tympani and eventually to the round window, causing it in the figure.) to bulge outward into the middle ear (See ● The pressure waves travel through the perilymph of the scala vestibuli, then the vestibular membrane, and then move into the endolymph inside the cochlear duct The pressure waves in the endolymph cause the basilar membrane to vibrate, which moves the hair cells of the spiral organ against the tectorial membrane This leads to bending of the stereocilia and ultimately to the generation of nerve impulses in first-order neurons in cochlear nerve fibers Sound waves of various frequencies cause certain regions of the basilar membrane to vibrate more intensely than other regions Each segment of the basilar membrane is “tuned” for Figure 17.22 Events in the stimulation of auditory receptors in the right ear The numbers correspond to the events listed in the text The cochlea has been uncoiled to more easily visualize the transmission of sound waves and their distortion of the vestibular and basilar membranes of the cochlear duct Hair cells of the spiral organ (organ of Corti) convert a mechanical vibration (stimulus) into an electrical signal (receptor potential) Incus Malleus Helicotrema Stapes vibrating in oval window Cochlea Sound waves Perilymph Scala tympani Scala vestibuli External auditory canal Basilar membrane Spiral organ (organ of Corti) Tectorial membrane Vestibular membrane Cochlear duct (contains endolymph) Tympanic membrane Secondary tympanic membrane vibrating in round window Middle ear Auditory tube Which part of the basilar membrane vibrates most vigorously in response to high-frequency (high-pitched) sounds? There are many visual resources within WileyPLUS, in addition to the art from your text These visual aids can help you master the topic you are studying Examples closely integrated with the reading material include animations, cadaver video clips, and Real Anatomy Views Anatomy Drill and Practice lets you test your knowledge of structures with simple-to-use drag-and-drop labeling exercises or fill-in-the-blank labeling You can drill and practice on these activities using illustrations from the text, cadaver photographs, histology micrographs, or lab models v JWCL316_fm_i-xxxiv.qxd 17/11/2010 21:23 Page vi N OT E S TO S T U D E N T S Exhibits Organize Complex Anatomy into Manageable Modules Many topics in this text have been organized into Exhibits that bring together all of the information and elements that you need to learn the complex terminology, anatomy, and the relevance of the anatomy into a simple-to-navigate content module You will find Exhibits for tissues, bones, joints, skeletal muscles, nerves, and blood vessels Most exhibits include the following: EXHIBIT 11.B Objective to focus your study Overview narrative of the structure(s) Table summarizing key features of the structure(s) Illustrations and photographs Checkpoint Question to assess your understanding Clinical Connection to provide relevance for learning the details Muscles of the Head That Move the Eyeballs (Extrinsic Eye Muscles) and Upper Eyelids (Figure 11.5) OBJECTIVE • Describe the origin, insertion, action, and innervation of the extrinsic eye muscles that move the eyeballs and upper eyelids Muscles that move the eyeballs are called extrinsic eye muscles because they originate outside the eyeballs (in the orbit) and insert on the outer surface of the sclera (“white of the eye”) (Figure 11.5) The extrinsic eye muscles are some of the fastest contracting and most precisely controlled skeletal muscles in the body Three pairs of extrinsic eye muscles control movements of the eyeballs: (1) superior and inferior recti, (2) lateral and medial recti, and (3) superior and inferior obliques The four recti muscles (superior, inferior, lateral, and medial) arise from a tendinous ring in the orbit and insert into the sclera of the eye As their names imply, the superior and inferior recti move the eyeballs superiorly and inferiorly; the lateral and medial recti move the eyeballs laterally and medially, respectively The actions of the oblique muscles cannot be deduced from their names The superior oblique muscle originates posteriorly near the tendinous ring, then passes anteriorly superior to the medial rectus muscle, and ends in a round tendon The tendon extends through a pulleylike loop of fibrocartilaginous tissue called the trochlea (ϭ pulley) on the anterior and medial part of the roof of the orbit Finally, the tendon turns and inserts on the posterolateral aspect of the eyeball Accordingly, the superior oblique muscle moves the eyeballs inferiorly and laterally The inferior oblique muscle originates on the maxilla at the anteromedial aspect of the floor of the orbit It then passes posteriorly and laterally and inserts on the posterolateral aspect of the eyeball Because of this arrangement, the inferior oblique muscle moves the eyeballs superiorly and laterally Unlike the recti and oblique muscles, the levator palpebrae superioris does not move the eyeballs, since its tendon passes the eyeball and inserts into the upper eyelid Rather, it raises the upper eyelids, that is, opens the eyes It is therefore an antagonist to the orbicularis oculi, EXHIBIT which closes the eyes CLINICAL CONNECTION | Strabismus 11.B Muscles of the Head That Move the Eyeballs (Extrinsic Eye Muscles) and Upper Eyelids (Figure 11.5) RELATING MUSCLES TO MOVEMENTS CONTINUED CHECKPOINT Strabismus (stra-BIZ-mus; strabismos ϭ squinting) is a condiWhich muscles that move the eyeballs contract and relax as Arrange tion in which the two eyeballs are not properly aligned This can be the muscles in this exhibit according to their actions on the eyeyou look to your left without moving your head? balls: hereditary or it can be due to birth injuries, poor attachments of the (1) elevation, (2) depression, (3) abduction, (4) adduction, (5) medial rotation, and (6) lateral rotation The same muscle may be menmuscles, problems with the brain’s control center, or localized disease tioned more than once Strabismus can be constant or intermittent In strabismus, each eye sends an image to a different area of the brain and because the brain usually ignores the messages sent by one of the eyes, the ignored eye becomes weaker; hence “lazy eye,” or amblyopia, develops External strabismus results when a lesion in the oculomotor (III) nerve causes Figure 11.5 Muscles of the head that move the eyeballs (extrinsic eye muscles) and upper eyelid the eyeball to move laterally when at rest, and results in an inability to move the eyeball medially and inferiorly A lesion in the abducens The extrinsic muscles of the eyeball are among the fastest contracting and most precisely controlled skeletal muscles in the (VI) nerve results in internal strabismus, a condition in which the eyebody ball moves medially when at rest and cannot move laterally Treatment options for strabismus depend on the specific type of Trochlea problem and include surgery, visual therapy (retraining the brain’s control INFERIOR OBLIQUE SUPERIOR RECTUS center), and orthoptics (eye muscle training to straighten the eyes) • SUPERIOR OBLIQUE Frontal bone LEVATOR PALPEBRAE SUPERIORIS (cut) Trochlea SUPERIOR RECTUS MUSCLE ORIGIN INSERTION ACTION INNERVATION MEDIAL RECTUS Superior rectus (rectus ϭ fascicles parallel to midline) Common tendinous ring (attached to orbit around optic foramen) Superior and central part of eyeballs Moves eyeballs superiorly (elevation) and medially (adduction), and rotates them medially Optic (II) nerve Oculomotor (III) nerve Inferior rectus Same as above Inferior and central part of eyeballs Moves eyeballs inferiorly (depression) and medially (adduction), and rotates them medially LATERAL RECTUS Oculomotor (III) nerve Abducens (VI) nerve LATERAL RECTUS Cornea Common tendinous ring SUPERIOR INFERIOR OBLIQUE RECTUS Sphenoid bone INFERIOR RECTUS Lateral rectus Same as above Lateral side of eyeballs Moves eyeballs laterally (abduction) Medial rectus Same as above Medial side of eyeballs Moves eyeballs medially (adduction) INFERIOR OBLIQUE Oculomotor (III) nerve Superior oblique (oblique ϭ fascicles diagonal to midline) Sphenoid bone, superior and medial to common tendinous ring in orbit Eyeball between superior and lateral recti Muscle inserts into superior and lateral surfaces of eyeball via tendon that passes through trochlea Moves eyeballs inferiorly (depression) and laterally (abduction), and rotates them medially Trochlear (IV) nerve Inferior oblique Maxilla in floor of orbit Eyeballs between inferior and lateral recti Moves eyeballs superiorly (elevation) and laterally (abduction), and rotates them laterally Levator palpebrae superioris (le-VA¯-tor PAL-pe-bre¯ soo-perЈ-e¯ -OR-is; palpebrae ϭ eyelids) Roof of orbit (lesser wing of sphenoid bone) Skin and tarsal plate of upper eyelids (opens eyes) Elevates upper eyelids Maxilla (a) Right lateral view of right eyeball (b) Movements of right eyeball in response to contraction of extrinsic muscles SUPERIOR OBLIQUE Oculomotor (III) nerve Frontal bone (cut) Oculomotor (III) nerve SUPERIOR RECTUS LEVATOR PALPEBRAE SUPERIORIS MEDIAL RECTUS LATERAL RECTUS E X H I B I T 11.B INFERIOR RECTUS CONTINUES INFERIOR OBLIQUE Zygomatic bone (cut) (c) Right lateral view of right eyeball How does the inferior oblique muscle move the eyeball superiorly and laterally? 380 vi MEDIAL RECTUS Eyeball EXHIBIT 11.B JWCL316_fm_i-xxxiv.qxd 18/11/2010 22:16 N OT E S Page vii TO S T U D E N T S Clinical Discussions Make Your Study Relevant The relevance of the anatomy and physiology that you are studying is best understood when you make the connection between normal structure and function and what happens when the body doesn’t work the way it should Throughout the chapters of the text you will find Clinical Connections that introduce you to interesting clinical perspectives related to the text discussion In CLINICAL CONNECTION | Arthroplasty addition, at the end of Joints that have been severely damaged by diseases such as tic such as polyethylene, and the femoral component is composed of arthritis, or by injury, may be replaced surgically with artificial joints a metal such as cobalt-chrome, titanium alloys, or stainless steel each body system chapin a procedure referred to as arthroplasty (AR-thro¯ -plas’-te¯; arthr-ϭ These materials are designed to withstand a high degree of stress and joint; plastyϭplastic repair of) Although most joints in the body can to prevent a response by the immune system Once the appropriate ter you will find the be repaired by arthroplasty, the ones most commonly replaced are acetabular and femoral components are selected, they are attached the hips, knees, and shoulders About 400,000 hip replacements and to the healthy portion of bone with acrylic cement, which forms an Disorders: Homeostatic 300,000 knee replacements are performed annually in the United interlocking mechanical bond States During the procedure, the ends of the damaged bones are reKnee replacements are actually a resurfacing of cartilage and, Imbalances section, moved and metal, ceramic, or plastic components are fixed in place like hip replacements, may be partial or total In a partial knee reThe goals of arthroplasty are to relieve pain and increase range of placement (PKR), also called a unicompartmental knee replacewhich includes concise motion ment, only one side of the knee joint is replaced Once the damaged discussions of major disPartial hip replacements involve only the femur Total hip recartilage is removed from the distal end of the femur, the femur is replacements involve both the acetabulum and head of the femur shaped and a metal femoral component is cemented in place Then eases and disorders (Figures A–C) The damaged portions of the acetabulum and the head the damaged cartilage from the proximal end of the tibia is removed, along with the meniscus The tibia is reshaped and fitted with a plasof the femur are replaced by prefabricated prostheses (artificial deThese provide answers tic tibial component that is cemented into place If the posterior survices) The acetabulum is shaped to accept the new socket, the head face of the patella is badly damaged, the patella is replaced with a of the femur is removed, and the center of the femur is shaped to fit to many of your quesplastic patellar component the femoral component The acetabular component consists of a plastions about medical problems The Medical Hip bone Terminology section Hip bone Artificial that follows includes acetabulum Reshaped Artificial Artificial acetabulum selected terms dealing femoral acetabulum head Head of femur with both normal and Artificial removed femoral pathological conditions head Artificial metal shaft Artificial metal shaft Shaft of femur Shaft of femur (A) Preparation for total hip replacement (B) Components of an artificial hip joint prior to implantation (C) Radiograph of an artificial hip joint WileyPLUS offers you opportunities for even further Clinical Connections with animated and interactive case studies that relate specifically to one body system Look for these under additional chapter resources as an interesting and engaging break from traditional study routines vii JWCL316_fm_i-xxxiv.qxd 17/11/2010 21:23 Page viii N OT E S TO S T U D E N T S Chapter Resources Help You Focus and Review Your book has a variety of special features that will make your time studying anatomy and physiology a more rewarding experience These have been developed based on feedback from students—like you—who have used previous editions of the text Their effectiveness is even further enhanced within WileyPLUS for Anatomy and Physiology Chapter Introductions set the stage for the content to come Each chapter starts with a succinct overview of the particular system’s role in maintaining homeostasis in your body, followed by an introduction to the chapter content This opening page concludes with a question that always begins with “Did you ever wonder…?” These questions will capture your interest and encourage you to find the answer in the chapter material to come Objectives at the start of each section help you focus on what is important as you read All of the content within WileyPLUS is tagged to these specific learning objectives so that you can organize your study or review what is still not clear in simple, more meaningful ways Checkpoint Questions at the end of each section help you assess if you have absorbed what you have read Take time to review these questions or answer them within the Practice section of each WileyPLUS concept module, where your answers will automatically be graded to let you know where you stand Mnemonics are a memory aid that can be particularly helpful when learning specific anatomical features Mnemonics are included throughout the text—some displayed in figures, tables, or Exhibits, and some included within the text discussion We encourage you not only to use the mnemonics provided, but also to create your own to help you learn the multitude of terms involved in your study of human anatomy Chapter Review and Resource Summary is a helpful table at the end of chapters that offers you a concise summary of the important concepts from the chapter and links each section to the media resources available in WileyPLUS for Anatomy and Physiology Self-Quiz Questions give you an opportunity to evaluate your understanding of the chapter as a whole Within WileyPLUS, use Progress Check to quiz yourself on individual or multiple chapters in preparation for exams or quizzes Critical Thinking Questions are word problems that allow you to apply the concepts you have studied in the chapter to specific situations Mastering the Language of Anatomy and Physiology Throughout the text we have included Pronunciations and, sometimes, Word Roots for many terms that may be new to you These appear in parentheses immediately following the new words The pronunciations are repeated in the Glossary at the back of the book Look at the words carefully and say them out loud several times Learning to pronounce a new word will help you remember it and make it a useful part of your medical vocabulary Take a few minutes to read the Pronunciation Key, found at the beginning of the Glossary at the end of this text, so it will be familiar as you encounter new words To provide more assistance in learning the language of anatomy, a full Glossary of terms with phonetic pronunciations appears at the end of the book The basic building blocks of medical terminology—Combining Forms, Word viii Roots, Prefixes, and Suffixes—are listed inside the back cover, accompanied by Eponyms, traditional terms that include reference to a person’s name, along with the current terminology WileyPLUS houses help for you in building your new language skills as well The Audio Glossary, which is always available to you, lets you hear all these new, unfamiliar terms pronounced Throughout the e-text, these terms can be clicked on and heard pronounced as you read In addition, you can use the helpful Mastering Vocabulary program, which creates electronic flashcards for you of the key terms within each chapter for practice, as well as take a self-quiz specifically on the terms introduced in each chapter JWCL316_c02_029-062.qxd 30 7/16/10 9:55 AM Page 30 CHAPTER • THE CHEMICAL LEVEL OF ORGANIZATION 2.1 HOW MATTER IS ORGANIZED OBJECTIVES • Identify the main chemical elements of the human body • Describe the structures of atoms, ions, molecules, free radicals, and compounds Chemical Elements Matter exists in three states: solid, liquid, and gas Solids, such as bones and teeth, are compact and have a definite shape and volume Liquids, such as blood plasma, have a definite volume and assume the shape of their container Gases, like oxygen and carbon dioxide, have neither a definite shape nor volume All forms of matter—both living and nonliving—are made up of a limited number of building blocks called chemical elements Each element is a substance that cannot be split into a simpler substance by ordinary chemical means Scientists now recognize 117 elements Of these, 92 occur naturally on Earth The rest have been produced from the natural elements using particle accelerators or nuclear reactors Each element is designated by a chemical sym- bol, one or two letters of the element’s name in English, Latin, or another language Examples of chemical symbols are H for hydrogen, C for carbon, O for oxygen, N for nitrogen, Ca for calcium, and Na for sodium (natrium ϭ sodium).* Twenty-six different chemical elements normally are present in your body Just four elements, called the major elements, constitute about 96% of the body’s mass: oxygen, carbon, hydrogen, and nitrogen Eight others, the lesser elements, contribute about 3.6% to the body’s mass: calcium, phosphorus (P), potassium (K), sulfur (S), sodium, chlorine (Cl), magnesium (Mg), and iron (Fe) An additional 14 elements—the trace elements—are present in tiny amounts Together, they account for the remaining about 0.4% of the body’s mass Several trace elements have important functions in the body For example, iodine is needed to make thyroid hormones The functions of some trace elements are unknown Table 2.1 lists the main chemical elements of the human body *The periodic table of elements, which lists all of the known chemical elements, can be found in Appendix B TABLE 2.1 Main Chemical Elements in the Body CHEMICAL ELEMENT (SYMBOL) MAJOR ELEMENTS % OF TOTAL BODY MASS SIGNIFICANCE (about 96) Oxygen (O) 65.0 Part of water and many organic (carbon-containing) molecules; used to generate ATP, a molecule used by cells to temporarily store chemical energy Carbon (C) 18.5 Forms backbone chains and rings of all organic molecules: carbohydrates, lipids (fats), proteins, and nucleic acids (DNA and RNA) Hydrogen (H) 9.5 Constituent of water and most organic molecules; ionized form (Hϩ) makes body fluids more acidic Nitrogen (N) 3.2 Component of all proteins and nucleic acids LESSER ELEMENTS (about 3.6) Calcium (Ca) 1.5 Contributes to hardness of bones and teeth; ionized form (Ca2ϩ) needed for blood clotting, release of some hormones, contraction of muscle, and many other processes Phosphorus (P) 1.0 Component of nucleic acids and ATP; required for normal bone and tooth structure Potassium (K) 0.35 Ionized form (Kϩ) is the most plentiful cation (positively charged particle) in intracellular fluid; needed to generate action potentials Sulfur (S) 0.25 Component of some vitamins and many proteins Sodium (Na) 0.2 Ionized form (Naϩ) is the most plentiful cation in extracellular fluid; essential for maintaining water balance; needed to generate action potentials Chlorine (Cl) 0.2 Ionized form (ClϪ) is the most plentiful anion (negatively charged particle) in extracellular fluid; essential for maintaining water balance Magnesium (Mg) 0.1 Ionized form (Mg2ϩ) needed for action of many enzymes, molecules that increase the rate of chemical reactions in organisms Iron (Fe) 0.005 Ionized forms (Fe2ϩ and Fe3ϩ) are part of hemoglobin (oxygen-carrying protein in red blood cells) and some enzymes (about 0.4) Aluminum (Al), boron (B), chromium (Cr), cobalt (Co), copper (Cu), fluorine (F), iodine (I), manganese (Mn), molybdenum (Mo), selenium (Se), silicon (Si), tin (Sn), vanadium (V), and zinc (Zn) TRACE ELEMENTS JWCL316_c02_029-062.qxd 7/15/10 7:46 AM Page 31 2.1 HOW MATTER IS ORGANIZED Structure of Atoms Each element is made up of atoms, the smallest units of matter that retain the properties and characteristics of the element Atoms are extremely small Two hundred thousand of the largest atoms would fit on the period at the end of this sentence Hydrogen atoms, the smallest atoms, have a diameter less than 0.1 nanometer (0.1 ϫ 10Ϫ9 m ϭ 0.0000000001 m), and the largest atoms are only five times larger Dozens of different subatomic particles compose individual atoms However, only three types of subatomic particles are important for understanding the chemical reactions in the human body: protons, neutrons, and electrons (Figure 2.1) The dense central core of an atom is its nucleus Within the nucleus are positively charged protons (pϩ) and uncharged (neutral) neutrons (n0) The tiny, negatively charged electrons (eϪ) move about in a large space surrounding the nucleus They not follow a fixed path or orbit but instead form a negatively charged “cloud” that envelops the nucleus (Figure 2.1a) Even though their exact positions cannot be predicted, specific groups of electrons are most likely to move about within certain regions around the nucleus These regions, called electron shells, are depicted as simple circles around the nucleus Because each electron shell can hold a specific number of electrons, the electron Figure 2.1 Two representations of the structure of an atom Electrons move about the nucleus, which contains neutrons and protons (a) In the electron cloud model of an atom, the shading represents the chance of finding an electron in regions outside the nucleus (b) In the electron shell model, filled circles represent individual electrons, which are grouped into concentric circles according to the shells they occupy Both models depict a carbon atom, with six protons, six neutrons, and six electrons An atom is the smallest unit of matter that retains the properties and characteristics of its element Protons (p+) Nucleus Neutrons (n0) Electrons (e–) (a) Electron cloud model (b) Electron shell model How are the electrons of carbon distributed between the first and second electron shells? 31 shell model best conveys this aspect of atomic structure (Figure 2.1b) The first electron shell (nearest the nucleus) never holds more than electrons The second shell holds a maximum of electrons, and the third can hold up to 18 electrons The electron shells fill with electrons in a specific order, beginning with the first shell For example, notice in Figure 2.2 that sodium (Na), which has 11 electrons total, contains electrons in the first shell, electrons in the second shell, and electron in the third shell The most massive element present in the human body is iodine, which has a total of 53 electrons: in the first shell, in the second shell, 18 in the third shell, 18 in the fourth shell, and in the fifth shell The number of electrons in an atom of an element always equals the number of protons Because each electron and proton carries one charge, the negatively charged electrons and the positively charged protons balance each other Thus, each atom is electrically neutral; its total charge is zero Atomic Number and Mass Number The number of protons in the nucleus of an atom is an atom’s atomic number Figure 2.2 shows that atoms of different elements have different atomic numbers because they have different numbers of protons For example, oxygen has an atomic number of because its nucleus has protons, and sodium has an atomic number of 11 because its nucleus has 11 protons The mass number of an atom is the sum of its protons and neutrons Because sodium has 11 protons and 12 neutrons, its mass number is 23 (Figure 2.2) Although all atoms of one element have the same number of protons, they may have different numbers of neutrons and thus different mass numbers Isotopes are atoms of an element that have different numbers of neutrons and therefore different mass numbers In a sample of oxygen, for example, most atoms have neutrons, and a few have or 10, but all have protons and electrons Most isotopes are stable, which means that their nuclear structure does not change over time The stable isotopes of oxygen are designated 16O, 17O, and 18O (or O-16, O-17, and O-18) As you may already have determined, the numbers indicate the mass number of each isotope As you will discover shortly, the number of electrons of an atom determines its chemical properties Although the isotopes of an element have different numbers of neutrons, they have identical chemical properties because they have the same number of electrons Certain isotopes called radioactive isotopes are unstable; their nuclei decay (spontaneously change) into a stable configuration Examples are H-3, C-14, O-15, and O-19 As they decay, these atoms emit radiation—either subatomic particles or packets of energy—and in the process often transform into a different element For example, the radioactive isotope of carbon, C-14, decays to N-14 The decay of a radioisotope may be as fast as a fraction of a second or as slow as millions of years The half-life of an isotope is the time required for half of the radioactive atoms in a sample of that isotope to decay into a more stable form The halflife of C-14, which is used to determine the age of organic samples, is about 5730 years; the half-life of I-131, an important clinical tool, is days JWCL316_c02_029-062.qxd 32 7/15/10 7:46 AM Page 32 CHAPTER • THE CHEMICAL LEVEL OF ORGANIZATION Figure 2.2 Atomic structures of several stable atoms The atoms of different elements have different atomic numbers because they have different numbers of protons First electron shell Second electron shell + 1p Hydrogen (H) Atomic number = Mass number = or Atomic mass = 1.01 + + 6p 6n Carbon (C) Atomic number = Mass number = 12 or 13 Atomic mass = 12.01 + 11p 12n Sodium (Na) Atomic number = 11 Mass number = 23 Atomic mass = 22.99 8p 8n Nitrogen (N) Atomic number = Mass number = 14 or 15 Atomic mass = 14.01 Fourth electron shell Third electron shell + 7p 7n + 17p 18n Chlorine (Cl) Atomic number = 17 Mass number = 35 or 37 Atomic mass = 35.45 Oxygen (O) Atomic number = Mass number = 16, 17, or 18 Atomic mass = 16.00 Fifth electron shell + + 19p 20n Potassium (K) Atomic number = 19 Mass number = 39, 40, or 41 Atomic mass = 39.10 53p 74n Iodine (I) Atomic number = 53 Mass number = 127 Atomic mass = 126.90 Atomic number = number of protons in an atom Mass number = number of protons and neutrons in an atom (boldface indicates most common isotope) Atomic mass = average mass of all stable atoms of a given element in daltons Which four of these elements are present most abundantly in living organisms? CLINICAL CONNECTION | Harmful and Beneficial Effects of Radiation Radioactive isotopes may have either harmful or helpful effects Their radiations can break apart molecules, posing a serious threat to the human body by producing tissue damage and/or causing various types of cancer Although the decay of naturally occurring radioactive isotopes typically releases just a small amount of radiation into the environment, localized accumulations can occur Radon-222, a colorless and odorless gas that is a naturally occurring radioactive breakdown product of uranium, may seep out of the soil and accumulate in buildings It is not only associated with many cases of lung cancer in smokers but has also been implicated in many cases of lung cancer in nonsmokers Beneficial effects of certain radioisotopes include their use in medical imaging procedures to diagnose and treat certain disorders Some radioisotopes can be used as tracers to follow the movement of certain substances through the body Thallium-201 is used to monitor blood flow through the heart during an exercise stress test Iodine-131 is used to detect cancer of the thyroid gland and to assess its size and activity, and may also be used to destroy part of an overactive thyroid gland Cesium-137 is used to treat advanced cervical cancer, and iridium-192 is used to treat prostate cancer • Atomic Mass The standard unit for measuring the mass of atoms and their subatomic particles is a dalton, also known as an atomic mass unit (amu) A neutron has a mass of 1.008 daltons, and a proton has a mass of 1.007 daltons The mass of an electron, at 0.0005 dalton, is almost 2000 times smaller than the mass of a neutron or proton The atomic mass (also called the atomic weight) of an element is the average mass of all its naturally occurring isotopes Typically, the atomic mass of an element is close to the mass number of its most abundant isotope Ions, Molecules, and Compounds As we discussed, atoms of the same element have the same number of protons The atoms of each element have a characteristic way of losing, gaining, or sharing their electrons when interacting with other atoms to achieve stability The way that electrons behave enables atoms in the body to exist in electrically charged forms called ions, or to join with each other into complex combinations called molecules If an atom either gives up or gains electrons, it becomes an ion An ion is an atom that has a positive or JWCL316_c02_029-062.qxd 7/15/10 7:46 AM Page 33 2.2 CHEMICAL BONDS negative charge because it has unequal numbers of protons and electrons Ionization is the process of giving up or gaining electrons An ion of an atom is symbolized by writing its chemical symbol followed by the number of its positive (ϩ) or negative (–) charges Thus, Ca2ϩ stands for a calcium ion that has two positive charges because it has lost two electrons When two or more atoms share electrons, the resulting combination is called a molecule (MOL-e-ku¯l) A molecular formula indicates the elements and the number of atoms of each element that make up a molecule A molecule may consist of two atoms of the same kind, such as an oxygen molecule (Figure 2.3a) The molecular formula for a molecule of oxygen is O2 The subscript indicates that the molecule contains two atoms of oxygen Two or more different kinds of atoms may also form a molecule, as in a water molecule (H2O) In H2O one atom of oxygen shares electrons with two atoms of hydrogen A compound is a substance that contains atoms of two or more different elements Most of the atoms in the body are joined into compounds Water (H2O) and sodium chloride (NaCl), common table salt, are compounds However, a molecule of oxygen (O2) is not a compound because it consists of atoms of only one element A free radical is an atom or group of atoms with an unpaired electron in the outermost shell A common example is superoxide, which is formed by the addition of an electron to an oxygen molecule (Figure 2.3b) Having an unpaired electron makes a free radical unstable, highly reactive, and destructive to nearby molecules Free radicals become stable by either giving up their unpaired electron to, or taking on an electron from, another molecule In so doing, free radicals may break apart important body molecules CLINICAL CONNECTION | Free Radicals and Antioxidants There are several sources of free radicals, including exposure to ultraviolet radiation in sunlight, exposure to x-rays, and some reactions that occur during normal metabolic processes Certain harmful substances, such as carbon tetrachloride (a solvent used in dry cleaning), also give rise to free radicals when they participate in metabolic reactions in the body Among the many disorders, diseases, and conditions linked to oxygen-derived free radicals are cancer, atherosclerosis, Alzheimer disease, emphysema, diabetes mellitus, cataracts, macular degeneration, rheumatoid arthritis, and deterioration associated with aging Consuming more antioxidants—substances that inactivate oxygen-derived free radicals—is thought to slow the pace of damage caused by free radicals Important dietary antioxidants include selenium, zinc, beta-carotene, and vitamins C and E Red, blue, or purple fruits and vegetables contain high levels of antioxidants • 33 Figure 2.3 Atomic structures of an oxygen molecule and a superoxide free radical A free radical has an unpaired electron in its outermost electron shell – O O O O Unpaired electron (a) Oxygen molecule (O2) (b) Superoxide free radical (O2–) What substances in the body can inactivate oxygen-derived free radicals? 2.2 CHEMICAL BONDS OBJECTIVES • Describe how valence electrons form chemical bonds • Distinguish among ionic, covalent, and hydrogen bonds The forces that hold together the atoms of a molecule or a compound are chemical bonds The likelihood that an atom will form a chemical bond with another atom depends on the number of electrons in its outermost shell, also called the valence shell An atom with a valence shell holding eight electrons is chemically stable, which means it is unlikely to form chemical bonds with other atoms Neon, for example, has eight electrons in its valence shell, and for this reason it does not bond easily with other atoms The valence shell of hydrogen and helium is the first electron shell, which holds a maximum of two electrons Because helium has two valence electrons, it too is stable and seldom bonds with other atoms Hydrogen, on the other hand, has only one valence electron (see Figure 2.2), so it binds readily with other atoms The atoms of most biologically important elements not have eight electrons in their valence shells Under the right conditions, two or more atoms can interact in ways that produce a chemically stable arrangement of eight valence electrons for each atom This chemical principle, called the octet rule (octet ϭ set of eight), helps explain why atoms interact in predictable ways One atom is more likely to interact with another atom if doing so will leave both with eight valence electrons For this to happen, an atom either empties its partially filled valence shell, fills it with donated electrons, or shares electrons with other atoms The way that valence electrons are distributed determines what kind of chemical bond results We will consider three types of chemical bonds: ionic bonds, covalent bonds, and hydrogen bonds CHECKPOINT List the names and chemical symbols of the 12 most abundant chemical elements in the human body What are the atomic number, mass number, and atomic mass of carbon? How are they related? Define isotopes and free radicals Ionic Bonds As you have already learned, when atoms lose or gain one or more valence electrons, ions are formed Positively and negatively charged ions are attracted to one another—opposites JWCL316_c02_029-062.qxd 34 11/08/2010 09:19 Page 34 CHAPTER • THE CHEMICAL LEVEL OF ORGANIZATION attract The force of attraction that holds together ions with opposite charges is an ionic bond Consider sodium and chlorine atoms, the components of common table salt Sodium has one valence electron (Figure 2.4a) If sodium loses this electron, it is left with the eight electrons in its second shell, which becomes the valence shell As a result, however, the total number of protons (11) exceeds the number of electrons (10) Thus, the sodium atom has become a cation (KAT-ı¯-on), or positively charged ion A sodium ion has a charge of 1ϩ and is written Naϩ By contrast, chlorine has seven valence electrons (Figure 2.4b) If chlorine gains an electron from a neighboring atom, it will have a complete octet in its third electron shell After gaining an electron, the total number of electrons (18) exceeds the number of protons (17), and the chlorine atom has become an anion (AN-ı¯-on), a negatively charged ion The ionic form of chlorine is called a chloride ion It has a charge of 1Ϫ and is written ClϪ When an atom of sodium donates its sole valence electron to an atom of chlorine, the resulting positive and negative charges pull both ions tightly together, forming an ionic bond (Figure 2.4c) The resulting compound is sodium chloride, written NaCl In general, ionic compounds exist as solids, with an orderly, repeating arrangement of the ions, as in a crystal of NaCl (Figure 2.4d) A crystal of NaCl may be large or small—the total number of ions can vary—but the ratio of Naϩ to ClϪ is always 1:1 In the body, ionic bonds are found mainly in teeth and bones, where they give great strength to these important structural tissues An ionic compound that breaks apart into positive and negative ions in solution is called an electrolyte (e-LEK-tro¯-lı¯ t) Most ions in the body are dissolved in body fluids as electrolytes, so named because their solutions can conduct an electric current (In Chapter 27 we will discuss the chemistry and importance of electrolytes.) Table 2.2 lists the names and symbols of common ions in the body TABLE 2.2 Common Ions in the Body CATIONS ANIONS NAME SYMBOL NAME SYMBOL Hydrogen ion Hϩ Fluoride ion FϪ Chloride ion ClϪ Iodide ion IϪ ϩ Sodium ion Na Potassium ion Kϩ Ammonium ion NH4 Hydroxide ion OHϪ Magnesium ion Mg2ϩ Bicarbonate ion HCO3Ϫ Oxide ion O2Ϫ Sulfate ion SO42Ϫ Phosphate ion PO43Ϫ ϩ 2ϩ Calcium ion Ca Iron(II) ion Fe2ϩ Iron(III) ion Fe 3ϩ Figure 2.4 Ions and ionic bond formation (a) A sodium atom can have a complete octet of electrons in its outermost shell by losing one electron (b) A chlorine atom can have a complete octet by gaining one electron (c) An ionic bond may form between oppositely charged ions (d) In a crystal of NaCl, each Naϩ is surrounded by six ClϪ In (a), (b), and (c), the electron that is lost or accepted is colored red An ionic bond is the force of attraction that holds together oppositely charged ions Electron accepted Na Na Cl Cl Ion Atom Ion Electron donated Atom (a) Sodium: valence electron Na (b) Chlorine: valence electrons Na+ Cl Cl – (c) Ionic bond in sodium chloride (NaCl) (d) Packing of ions in a crystal of sodium chloride What are cations and anions? JWCL316_c02_029-062.qxd 7/15/10 7:46 AM Page 35 2.2 CHEMICAL BONDS 35 of the same element or between atoms of different elements They are the most common chemical bonds in the body, and the compounds that result from them form most of the body’s structures A single covalent bond results when two atoms share one electron pair For example, a molecule of hydrogen forms when two hydrogen atoms share their single valence electrons (Figure 2.5a), which allows both atoms to have a full valence shell at Covalent Bonds When a covalent bond forms, two or more atoms share electrons rather than gaining or losing them Atoms form a covalently bonded molecule by sharing one, two, or three pairs of valence electrons The larger the number of electron pairs shared between two atoms, the stronger the covalent bond Covalent bonds may form between atoms Figure 2.5 Covalent bond formation The red electrons are shared equally in (a)–(d) and unequally in (e) In writing the structural formula of a covalently bonded molecule, each straight line between the chemical symbols for two atoms denotes a pair of shared electrons In molecular formulas, the number of atoms in each molecule is noted by subscripts In a covalent bond, two atoms share one, two, or three pairs of valence electrons STRUCTURAL FORMULA DIAGRAMS OF ATOMIC AND MOLECULAR STRUCTURE + H H Hydrogen atoms (a) + O O + N O H H2 O O O O2 N N N2 Oxygen molecule N N Nitrogen atoms (c) H Hydrogen molecule Oxygen atoms (b) H H MOLECULAR FORMULA N Nitrogen molecule H H H H C + C H H H H C H CH4 H H (d) Carbon atom H Methane molecule Hydrogen atoms δ+ H H H O + δ– H H (e) Oxygen atom Hydrogen atoms H2O O O δ+ Water molecule What is the principal difference between an ionic bond and a covalent bond? H JWCL316_c02_029-062.qxd 36 7/15/10 7:46 AM Page 36 CHAPTER • THE CHEMICAL LEVEL OF ORGANIZATION least part of the time A double covalent bond results when two atoms share two pairs of electrons, as happens in an oxygen molecule (Figure 2.5b) A triple covalent bond occurs when two atoms share three pairs of electrons, as in a molecule of nitrogen (Figure 2.5c) Notice in the structural formulas for covalently bonded molecules in Figure 2.5 that the number of lines between the chemical symbols for two atoms indicates whether the bond is a single (O), double (P), or triple (q) covalent bond The same principles of covalent bonding that apply to atoms of the same element also apply to covalent bonds between atoms of different elements The gas methane (CH4) contains covalent bonds formed between the atoms of two different elements, one carbon and four hydrogens (Figure 2.5d) The valence shell of the carbon atom can hold eight electrons but has only four of its own The single electron shell of a hydrogen atom can hold two electrons, but each hydrogen atom has only one of its own A methane molecule contains four separate single covalent bonds Each hydrogen atom shares one pair of electrons with the carbon atom In some covalent bonds, two atoms share the electrons equally—one atom does not attract the shared electrons more strongly than the other atom This type of bond is a nonpolar covalent bond The bonds between two identical atoms are always nonpolar covalent bonds (Figure 2.5a–c) The bonds between carbon and hydrogen atoms are also nonpolar, such as the four C—H bonds in a methane molecule (Figure 2.5d) In a polar covalent bond, the sharing of electrons between two atoms is unequal—the nucleus of one atom attracts the shared electrons more strongly than the nucleus of the other atom When polar covalent bonds form, the resulting molecule has a partial negative charge near the atom that attracts electrons more strongly This atom has greater electronegativity, the power to attract electrons to itself At least one other atom in the molecule then will have a partial positive charge The partial charges are indicated by a lowercase Greek delta with a minus or plus sign: ␦Ϫ or ␦ϩ A very important example of a polar covalent bond in living systems is the bond between oxygen and hydrogen in a molecule of water (Figure 2.5e); in this molecule, the nucleus of the oxygen atom attracts the electrons more strongly than the nuclei of the hydrogen atoms, so the oxygen atom is said to have greater electronegativity Later in the chapter, we will see how polar covalent bonds allow water to dissolve many molecules that are important to life Bonds between nitrogen and hydrogen and those between oxygen and carbon are also polar bonds rather than from sharing of electrons as in covalent bonds, or the loss or gain of electrons as in ionic bonds Hydrogen bonds are weak compared to ionic and covalent bonds Thus, they cannot bind atoms into molecules However, hydrogen bonds establish important links between molecules or between different parts of a large molecule, such as a protein or nucleic acid (both discussed later in this chapter) The hydrogen bonds that link neighboring water molecules give water considerable cohesion, the tendency of like particles to stay together The cohesion of water molecules creates a very high surface tension, a measure of the difficulty of stretching or breaking the surface of a liquid At the boundary between water and air, water’s surface tension is very high because the water molecules are much more attracted to one another than they are attracted to molecules in the air This is readily seen when a spider walks on water or a leaf floats on water The influence of water’s surface tension on the body can be seen in the way it increases the work required for breathing A thin film of watery fluid coats the air sacs of the lungs So, each inhalation must have enough force to overcome the opposing effect of surface tension as the air sacs stretch and enlarge when taking in air Even though single hydrogen bonds are weak, very large molecules may contain thousands of these bonds Acting collectively, hydrogen bonds provide considerable strength and stability and help determine the three-dimensional shape of large molecules As you will see later in this chapter, a large molecule’s shape determines how it functions Figure 2.6 Hydrogen bonding among water molecules Each water molecule forms hydrogen bonds (indicated by dotted lines) with three to four neighboring water molecules Hydrogen bonds occur because hydrogen atoms in one water molecule are attracted to the partial negative charge of the oxygen atom in another water molecule δ H O Hydrogen Bonds The polar covalent bonds that form between hydrogen atoms and other atoms can give rise to a third type of chemical bond, a hydrogen bond (Figure 2.6) A hydrogen bond forms when a hydrogen atom with a partial positive charge (␦ϩ) attracts the partial negative charge (␦Ϫ) of neighboring electronegative atoms, most often larger oxygen or nitrogen atoms Thus, hydrogen bonds result from attraction of oppositely charged parts of molecules Hydrogen bonds + H δ+ δ– Why would you expect ammonia (NH3) to form hydrogen bonds with water molecules? JWCL316_c02_029-062.qxd 7/15/10 7:46 AM Page 37 2.3 CHEMICAL REACTIONS CHECKPOINT Which electron shell is the valence shell of an atom, and what is its significance? Compare the properties of ionic, covalent, and hydrogen bonds What information is conveyed when you write the molecular or structural formula for a molecule? 2.3 CHEMICAL REACTIONS OBJECTIVES • • • • Define a chemical reaction Describe the various forms of energy Compare exergonic and endergonic chemical reactions Describe the role of activation energy and catalysts in chemical reactions • Describe synthesis, decomposition, exchange, and reversible reactions A chemical reaction occurs when new bonds form or old bonds break between atoms Chemical reactions are the foundation of all life processes, and as we have seen, the interactions of valence electrons are the basis of all chemical reactions Consider how hydrogen and oxygen molecules react to form water molecules (Figure 2.7) The starting substances—two H2 and one O2—are known as the reactants The ending substances—two molecules of H2O—are the products The arrow in the figure indicates the direction in which the reaction proceeds In a chemical reaction, the total mass of the reactants equals the total mass of the products Thus, the number of atoms of each element is the same before and after the reaction However, because the atoms are rearranged, the reactants and products have different chemical properties Through thousands of different chemical reactions, body structures are built and body functions are carried out The Figure 2.7 The chemical reaction between two hydrogen molecules (H2) and one oxygen molecule (O2) to form two molecules of water (H2O) Note that the reaction occurs by breaking old bonds and making new bonds The number of atoms of each element is the same before and after a chemical reaction H H H H H O + O O O2 H2 Reactants H O H H H2O Products Why does this reaction require two molecules of H2? 37 term metabolism refers to all the chemical reactions occurring in the body Forms of Energy and Chemical Reactions Each chemical reaction involves energy changes Energy (en- ϭ in; -ergy ϭ work) is the capacity to work Two principal forms of energy are potential energy, energy stored by matter due to its position, and kinetic energy, the energy associated with matter in motion For example, the energy stored in water behind a dam or in a person poised to jump down some steps is potential energy When the gates of the dam are opened or the person jumps, potential energy is converted into kinetic energy Chemical energy is a form of potential energy that is stored in the bonds of compounds and molecules The total amount of energy present at the beginning and end of a chemical reaction is the same Although energy can be neither created nor destroyed, it may be converted from one form to another This principle is known as the law of conservation of energy For example, some of the chemical energy in the foods we eat is eventually converted into various forms of kinetic energy, such as mechanical energy used to walk and talk Conversion of energy from one form to another generally releases heat, some of which is used to maintain normal body temperature Energy Transfer in Chemical Reactions Chemical bonds represent stored chemical energy, and chemical reactions occur when new bonds are formed or old bonds are broken between atoms The overall reaction may either release energy or absorb energy Exergonic reactions (ex- ϭ out) release more energy than they absorb By contrast, endergonic reactions (end- ϭ within) absorb more energy than they release A key feature of the body’s metabolism is the coupling of exergonic reactions and endergonic reactions Energy released from an exergonic reaction often is used to drive an endergonic one In general, exergonic reactions occur as nutrients, such as glucose, are broken down Some of the energy released may be trapped in the covalent bonds of adenosine triphosphate (ATP), which we describe more fully later in this chapter If a molecule of glucose is completely broken down, the chemical energy in its bonds can be used to produce as many as 38 molecules of ATP The energy transferred to the ATP molecules is then used to drive endergonic reactions needed to build body structures, such as muscles and bones The energy in ATP is also used to the mechanical work involved in the contraction of muscle or the movement of substances into or out of cells Activation Energy Because particles of matter such as atoms, ions, and molecules have kinetic energy, they are continuously moving and colliding with one another A sufficiently forceful collision can disrupt the movement of valence electrons, causing an existing chemical bond to break or a new one to form The collision energy needed to break the chemical bonds of the reactants is called the JWCL316_c02_029-062.qxd 7:46 AM Page 38 CHAPTER • THE CHEMICAL LEVEL OF ORGANIZATION activation energy of the reaction (Figure 2.8) This initial energy “investment” is needed to start a reaction The reactants must absorb enough energy for their chemical bonds to become unstable and their valence electrons to form new combinations Then, as new bonds form, energy is released to the surroundings Both the concentration of particles and the temperature influence the chance that a collision will occur and cause a chemical reaction • Concentration The more particles of matter present in a confined space, the greater the chance that they will collide (think of people crowding into a subway car at rush hour) The concentration of particles increases when more are added to a given space or when the pressure on the space increases, which forces the particles closer together so that they collide more often • Temperature As temperature rises, particles of matter move about more rapidly Thus, the higher the temperature of matter, the more forcefully particles will collide, and the greater the chance that a collision will produce a reaction Catalysts As we have seen, chemical reactions occur when chemical bonds break or form after atoms, ions, or molecules collide with one another Body temperature and the concentrations of molecules in body fluids, however, are far too low for most chemical reactions to occur rapidly enough to maintain life Raising the temperature Figure 2.9 Comparison of energy needed for a chemical reaction to proceed with a catalyst (blue curve) and without a catalyst (red curve) Catalysts speed up chemical reactions by lowering the activation energy Activation energy needed without catalyst Activation energy needed with catalyst Potential energy 38 7/15/10 Energy of reactants Energy of products Progress of the reaction Does a catalyst change the potential energies of the products and reactants? Figure 2.8 Activation energy Potential energy Activation energy is the energy needed to break chemical bonds in the reactant molecules so a reaction can start Activation energy Energy absorbed to start reaction Energy released as new bonds form Energy of reactants Energy of products Progress of the reaction Why is the reaction illustrated here exergonic? and the number of reacting particles of matter in the body could increase the frequency of collisions and thus increase the rate of chemical reactions, but doing so could also damage or kill the body’s cells Substances called catalysts solve this problem Catalysts are chemical compounds that speed up chemical reactions by lowering the activation energy needed for a reaction to occur (Figure 2.9) The most important catalysts in the body are enzymes, which we will discuss later in this chapter A catalyst does not alter the difference in potential energy between the reactants and the products Rather, it lowers the amount of energy needed to start the reaction For chemical reactions to occur, some particles of matter— especially large molecules—not only must collide with sufficient force, but they must hit one another at precise spots A catalyst helps to properly orient the colliding particles Thus, they interact at the spots that make the reaction happen Although the action of a catalyst helps to speed up a chemical reaction, the catalyst itself is unchanged at the end of the reaction A single catalyst molecule can assist one chemical reaction after another Types of Chemical Reactions After a chemical reaction takes place, the atoms of the reactants are rearranged to yield products with new chemical properties JWCL316_c02_029-062.qxd 7/16/10 10:01 AM Page 39 2.3 CHEMICAL REACTIONS 39 In this section we will look at the types of chemical reactions common to all living cells Once you have learned them, you will be able to understand the chemical reactions so important to the operation of the human body that are discussed throughout the book The bonds between A and B and between C and D break (decomposition), and new bonds then form (synthesis) between A and D and between B and C An example of an exchange reaction is Synthesis Reactions—Anabolism When two or more atoms, ions, or molecules combine to form new and larger molecules, the processes are called synthesis reactions The word synthesis means “to put together.” A synthesis reaction can be expressed as follows: Notice that the ions in both compounds have “switched partners”: The hydrogen ion (Hϩ) from HCl has combined with the bicarbonate ion (HCO3Ϫ) from NaHCO3, and the sodium ion (Naϩ) from NaHCO3 has combined with the chloride ion (ClϪ) from HCl A ϩ Atom, ion, or molecule A B Combine to form AB Atom, ion, or molecule B New molecule AB One example of a synthesis reaction is the reaction between two hydrogen molecules and one oxygen molecule to form two molecules of water (see Figure 2.7) Another example of a synthesis reaction is the formation of ammonia from nitrogen and hydrogen: N2 One nitrogen molecule ϩ 3H2 Combine to form Three hydrogen molecules 2NH3 Decomposition Reactions—Catabolism Decomposition reactions split up large molecules into smaller atoms, ions, or molecules A decomposition reaction is expressed as follows: Breaks down into Molecule AB A Atom, ion, or molecule A ϩ B Atom, ion, or molecule B The decomposition reactions that occur in your body are collectively referred to as catabolism (ka-TAB-o¯-lizm) Overall, catabolic reactions are usually exergonic because they release more energy than they absorb For instance, the series of reactions that break down glucose to pyruvic acid, with the net production of two molecules of ATP, are important catabolic reactions in the body These reactions will be discussed in Chapter 25 Exchange Reactions Many reactions in the body are exchange reactions; they consist of both synthesis and decomposition reactions One type of exchange reaction works like this: AB ϩ CD ϩ NaHCO3 AD ϩ BC H2CO3 ϩ Sodium bicarbonate Carbonic acid NaCl Sodium chloride Reversible Reactions Some chemical reactions proceed in only one direction, from reactants to products, as previously indicated by the single arrows Other chemical reactions may be reversible In a reversible reaction, the products can revert to the original reactants A reversible reaction is indicated by two half-arrows pointing in opposite directions: Breaks down into AB Combines to form AϩB Some reactions are reversible only under special conditions: Water Two ammonia molecules All the synthesis reactions that occur in your body are collectively referred to as anabolism (a-NAB-o¯-lizm) Overall, anabolic reactions are usually endergonic because they absorb more energy than they release Combining simple molecules like amino acids (discussed shortly) to form large molecules such as proteins is an example of anabolism AB HCl Hydrochloric acid AB Heat AϩB In that case, whatever is written above or below the arrows indicates the condition needed for the reaction to occur In these reactions, AB breaks down into A and B only when water is added, and A and B react to produce AB only when heat is applied Many reversible reactions in the body require catalysts called enzymes Often, different enzymes guide the reactions in opposite directions Oxidation–Reduction Reactions You will learn in Chapter 25 that chemical reactions called oxidation–reduction reactions are essential to life, since they are the reactions that break down food molecules to produce energy These reactions are concerned with the transfer of electrons between atoms and molecules Oxidation refers to the loss of electrons, and in the process the oxidized substance releases energy Reduction refers to the gain of electrons, and in the process the reduced substance gains energy Oxidation–reduction reactions are always parallel; when one substance is oxidized, another is reduced at the same time When a food molecule, such as glucose, is oxidized, the energy produced is used by a cell to carry out its various functions CHECKPOINT What is the relationship between reactants and products in a chemical reaction? Compare potential energy and kinetic energy How catalysts affect activation energy? 10 How are anabolism and catabolism related to synthesis and decomposition reactions, respectively? 11 Why are oxidation–reduction reactions important? JWCL316_c02_029-062.qxd 40 7/16/10 9:56 AM Page 40 CHAPTER • THE CHEMICAL LEVEL OF ORGANIZATION 2.4 INORGANIC COMPOUNDS AND SOLUTIONS OBJECTIVES • Describe the properties of water and those of inorganic acids, bases, and salts • Distinguish among solutions, colloids, and suspensions • Define pH and explain the role of buffer systems in homeostasis Most of the chemicals in your body exist in the form of compounds Biologists and chemists divide these compounds into two principal classes: inorganic compounds and organic compounds Inorganic compounds usually lack carbon and are structurally simple Their molecules also have only a few atoms and cannot be used by cells to perform complicated biological functions They include water and many salts, acids, and bases Inorganic compounds may have either ionic or covalent bonds Water makes up 55–60% of a lean adult’s total body mass; all other inorganic compounds combined add 1–2% Examples of inorganic compounds that contain carbon are carbon dioxide (CO2), bicarbonate ion (HCO3Ϫ), and carbonic acid (H2CO3) Organic compounds always contain carbon, usually contain hydrogen, and always have covalent bonds Most are large molecules and many are made up of long chains of carbon atoms Organic compounds make up the remaining 38–43% of the human body lute solution of water (the solvent) plus small amounts of salts (the solutes) The versatility of water as a solvent for ionized or polar substances is due to its polar covalent bonds and its bent shape, which allows each water molecule to interact with several neighboring ions or molecules Solutes that are charged or contain polar covalent bonds are hydrophilic (hydro- ϭ water; -philic ϭ loving), which means they dissolve easily in water Common examples of hydrophilic solutes are sugar and salt Molecules that contain mainly nonpolar covalent bonds, by contrast, are hydrophobic (-phobic ϭ fearing) They are not very water soluble Examples of hydrophobic compounds include animal fats and vegetable oils To understand the dissolving power of water, consider what happens when a crystal of a salt such as sodium chloride (NaCl) is placed in water (Figure 2.10) The electronegative oxygen Figure 2.10 How polar water molecules dissolve salts and polar substances When a crystal of sodium chloride is placed in water, the slightly negative oxygen end (red) of water molecules is attracted to the positive sodium ions (Naϩ), and the slightly positive hydrogen portions (gray) of water molecules are attracted to the negative chloride ions (ClϪ) In addition to dissolving sodium chloride, water also causes it to dissociate, or separate into charged particles, which is discussed shortly Water is a versatile solvent because its polar covalent bonds, in which electrons are shared unequally, create positive and negative regions Water Water is the most important and abundant inorganic compound in all living systems Although you might be able to survive for weeks without food, without water you would die in a matter of days Nearly all the body’s chemical reactions occur in a watery medium Water has many properties that make it such an indispensable compound for life We have already mentioned the most important property of water, its polarity—the uneven sharing of valence electrons that confers a partial negative charge near the one oxygen atom and two partial positive charges near the two hydrogen atoms in a water molecule (see Figure 2.5e) This property alone makes water an excellent solvent for other ionic or polar substances, gives water molecules cohesion (the tendency to stick together), and allows water to resist temperature changes Water as a Solvent In medieval times people searched in vain for a “universal solvent,” a substance that would dissolve all other materials They found nothing that worked as well as water Although it is the most versatile solvent known, water is not the universal solvent sought by medieval alchemists If it were, no container could hold it because it would dissolve all potential containers! What exactly is a solvent? In a solution, a substance called the solvent dissolves another substance called the solute Usually there is more solvent than solute in a solution For example, your sweat is a di- H H O δ– δ+ H δ+ H δ– Na δ– + δ– δ– δ– O Water molecule δ– Hydrated sodium ion Na+ H O Cl– H δ+ Crystal of NaCl δ+ δ+ δ+ Cl – δ δ+ + Hydrated chloride ion Table sugar (sucrose) easily dissolves in water but is not an electrolyte Is it likely that all the covalent bonds between atoms in table sugar are nonpolar bonds? Why or why not? JWCL316_c02_029-062.qxd 7/15/10 7:46 AM Page 41 2.4 INORGANIC COMPOUNDS AND SOLUTIONS atom in water molecules attracts the sodium ions (Naϩ), and the electropositive hydrogen atoms in water molecules attract the chloride ions (ClϪ) Soon, water molecules surround and separate Naϩ and ClϪ ions from each other at the surface of the crystal, breaking the ionic bonds that held NaCl together The water molecules surrounding the ions also lessen the chance that Naϩ and ClϪ will come together and re-form an ionic bond The ability of water to form solutions is essential to health and survival Because water can dissolve so many different substances, it is an ideal medium for metabolic reactions Water enables dissolved reactants to collide and form products Water also dissolves waste products, which allows them to be flushed out of the body in the urine Water in Chemical Reactions Water serves as the medium for most chemical reactions in the body and participates as a reactant or product in certain reactions During digestion, for example, decomposition reactions break down large nutrient molecules into smaller molecules by the addition of water molecules This type of reaction is called hydrolysis (hı¯-DROL-i-sis; -lysis ϭ to loosen or break apart) Hydrolysis reactions enable dietary nutrients to be absorbed into the body By contrast, when two smaller molecules join to form a larger molecule in a dehydration synthesis reaction (de- ϭ from, down, or out; hydra- ϭ water), a water molecule is one of the products formed As you will see later in the chapter, such reactions occur during synthesis of proteins and other large molecules (for example, see Figure 2.21) Thermal Properties of Water In comparison to most substances, water can absorb or release a relatively large amount of heat with only a modest change in its own temperature For this reason, water is said to have a high heat capacity The reason for this property is the large number of hydrogen bonds in water As water absorbs heat energy, some of the energy is used to break hydrogen bonds Less energy is then left over to increase the motion of water molecules, which would increase the water’s temperature The high heat capacity of water is the reason it is used in automobile radiators; it cools the engine by absorbing heat without its own temperature rising to an unacceptably high level The large amount of water in the body has a similar effect: It lessens the impact of environmental temperature changes, helping to maintain the homeostasis of body temperature Water also requires a large amount of heat to change from a liquid to a gas Its heat of vaporization is high As water evaporates from the surface of the skin, it removes a large quantity of heat, providing an important cooling mechanism Water as a Lubricant Water is a major component of mucus and other lubricating fluids throughout the body Lubrication is especially necessary in the chest (pleural and pericardial cavities) and abdomen (peritoneal cavity), where internal organs touch and slide over one another It 41 is also needed at joints, where bones, ligaments, and tendons rub against one another Inside the gastrointestinal tract, mucus and other watery secretions moisten foods, which aids their smooth passage through the digestive system Solutions, Colloids, and Suspensions A mixture is a combination of elements or compounds that are physically blended together but not bound by chemical bonds For example, the air you are breathing is a mixture of gases that includes nitrogen, oxygen, argon, and carbon dioxide Three common liquid mixtures are solutions, colloids, and suspensions Once mixed together, solutes in a solution remain evenly dispersed among the solvent molecules Because the solute particles in a solution are very small, a solution looks clear and transparent A colloid differs from a solution mainly because of the size of its particles The solute particles in a colloid are large enough to scatter light, just as water droplets in fog scatter light from a car’s headlight beams For this reason, colloids usually appear translucent or opaque Milk is an example of a liquid that is both a colloid and a solution: The large milk proteins make it a colloid, whereas calcium salts, milk sugar (lactose), ions, and other small particles are in solution The solutes in both solutions and colloids not settle out and accumulate on the bottom of the container In a suspension, by contrast, the suspended material may mix with the liquid or suspending medium for some time, but eventually it will settle out Blood is an example of a suspension When freshly drawn from the body, blood has an even, reddish color After blood sits for a while in a test tube, red blood cells settle out of the suspension and drift to the bottom of the tube (see Figure 19.1a) The upper layer, the liquid portion of blood, appears pale yellow and is called blood plasma Blood plasma is both a solution of ions and other small solutes and a colloid due to the presence of larger plasma proteins The concentration of a solution may be expressed in several ways One common way is by a mass per volume percentage, which gives the relative mass of a solute found in a given volume of solution For example, you may have seen the following on the label of a bottle of wine: “Alcohol 14.1% by volume.” Another way expresses concentration in units of moles per liter (mol/L), which relate to the total number of molecules in a given volume of solution A mole is the amount of any substance that has a mass in grams equal to the sum of the atomic masses of all its atoms For example, mole of the element chlorine (atomic mass ϭ 35.45) is 35.45 grams and mole of the salt sodium chloride (NaCl) is 58.44 grams (22.99 for Na ϩ 35.45 for Cl) Just as a dozen always means 12 of something, a mole of anything has the same number of particles: 6.023 ϫ 1023 This huge number is called Avogadro’s number Thus, measurements of substances that are stated in moles tell us about the numbers of atoms, ions, or molecules present This is important when chemical reactions are occurring because each reaction requires a set number of JWCL316_c02_029-062.qxd 42 10/11/10 1:20 PM Page 42 CHAPTER • THE CHEMICAL LEVEL OF ORGANIZATION TABLE 2.3 Percentage and Molarity DEFINITION EXAMPLE Percentage (mass per volume) Number of grams of a substance per 100 milliliters (mL) of solution To make a 10% NaCl solution, take 10 g of NaCl and add enough water to make a total of 100 mL of solution Molarity: moles (mol) per liter A molar (1 M) solution ϭ mole of a solute in liter of solution To make a molar (1 M) solution of NaCl, dissolve mole of NaCl (58.44 g) in enough water to make a total of liter of solution atoms of specific elements Table 2.3 describes these ways of expressing concentration Inorganic Acids, Bases, and Salts When inorganic acids, bases, or salts dissolve in water, they dis¯ T); that is, they separate into ions and besociate (disЈ-so¯-se¯ -A come surrounded by water molecules An acid (Figure 2.11a) is a substance that dissociates into one or more hydrogen ions (Hϩ) and one or more anions Because Hϩ is a single proton with one positive charge, an acid is also referred to as a proton donor A base, by contrast (Figure 2.11b), removes Hϩ from a solution and is therefore a proton acceptor Many bases dissociate into one or more hydroxide ions (OHϪ) and one or more cations A salt, when dissolved in water, dissociates into cations and anions, neither of which is Hϩ or OHϪ (Figure 2.11c) In the body, salts such as potassium chloride are electrolytes that are im- Figure 2.11 Dissociation of inorganic acids, bases, and salts Dissociation is the separation of inorganic acids, bases, and salts into ions in a solution HCl H + Cl – KOH K + OH – KCl K+ Cl portant for carrying electrical currents (ions flowing from one place to another), especially in nerve and muscular tissues The ions of salts also provide many essential chemical elements in intracellular and extracellular fluids such as blood, lymph, and the interstitial fluid of tissues Acids and bases react with one another to form salts For example, the reaction of hydrochloric acid (HCl) and potassium hydroxide (KOH), a base, produces the salt potassium chloride (KCl) and water (H2O) This exchange reaction can be written as follows: HCl ϩ KOH Acid Base Hϩ ϩ ClϪ ϩ Kϩ ϩ OHϪ Dissociated ions KCl ϩ H2O Salt Water Acid–Base Balance: The Concept of pH To ensure homeostasis, intracellular and extracellular fluids must contain almost balanced quantities of acids and bases The more hydrogen ions (Hϩ) dissolved in a solution, the more acidic the solution; the more hydroxide ions (OHϪ), the more basic (alkaline) the solution The chemical reactions that take place in the body are very sensitive to even small changes in the acidity or alkalinity of the body fluids in which they occur Any departure from the narrow limits of normal Hϩ and OHϪ concentrations greatly disrupts body functions A solution’s acidity or alkalinity is expressed on the pH scale, which extends from to 14 (Figure 2.12) This scale is based on the concentration of Hϩ in moles per liter A pH of means that a solution contains one ten-millionth (0.0000001) of a mole of hydrogen ions per liter The number 0.0000001 is written as ϫ 10Ϫ7 in scientific notation, which indicates that the number is with the decimal point moved seven places to the left To convert this value to pH, the negative exponent (–7) is changed to a positive number (7) A solution with a Hϩ concentration of 0.0001 (10Ϫ4) moles per liter has a pH of 4; a solution with a Hϩ concentration of 0.000000001 (10Ϫ9) moles per liter has a pH of 9; and so on It is important to realize that a change of one whole number on the pH scale represents a tenfold change in the number of Hϩ A pH of denotes 10 times more Hϩ than a pH of 7, and a pH of indicates 10 times fewer Hϩ than a pH of and 100 times fewer Hϩ than a pH of The midpoint of the pH scale is 7, where the concentrations of Hϩ and OHϪ are equal A substance with a pH of 7, such as pure water, is neutral A solution that has more Hϩ than OHϪ is an acidic solution and has a pH below A solution that has more OHϪ than Hϩ is a basic (alkaline) solution and has a pH above – Maintaining pH: Buffer Systems (a) Acid (b) Base (c) Salt The compound CaCO3 (calcium carbonate) dissociates into a calcium ion (Ca2ϩ) and a carbonate ion (CO32Ϫ) Is it an acid, a base, or a salt? What about H2SO4, which dissociates into two Hϩ and one SO42Ϫ? Although the pH of body fluids may differ, as we have discussed, the normal limits for each fluid are quite narrow Table 2.4 shows the pH values for certain body fluids along with those of some common substances outside the body Homeostatic mechanisms maintain the pH of blood between 7.35 and 7.45, which is slightly more basic than pure water You will learn in Chapter 27 that if the JWCL316_c02_029-062.qxd 7/15/10 7:47 AM Page 43 2.4 INORGANIC COMPOUNDS AND SOLUTIONS 43 Figure 2.12 The pH scale A pH below indicates an acidic solution—more Hϩ than OHϪ A pH above indicates a basic (alkaline) solution; that is, there are more OHϪ than Hϩ The lower the numerical value of the pH, the more acidic is the solution because the Hϩ concentration becomes progressively greater The higher the pH, the more basic the solution [OH–] –14 10 10 –13 10 –12 –11 10 10 –10 10 –9 10 –8 10 –7 –6 10 10 –5 –4 10 10 –3 –2 10 10 –1 10 (moles/liter) [H+] 10 10 pH –1 10 –2 10 –3 10 –4 –5 10 10 INCREASINGLY ACIDIC –6 10 –7 10 –8 10 –9 –10 10 10 10 –11 11 10 –12 12 –13 –14 10 10 13 14 INCREASINGLY BASIC (ALKALINE) NEUTRAL At pH (neutrality), the concentrations of Hϩ and OHϪ are equal (10Ϫ7 mol/liter) What are the concentrations of Hϩ and OHϪ at pH 6? Which pH is more acidic, 6.82 or 6.91? Which pH is closer to neutral, 8.41 or 5.59? TABLE 2.4 pH Values of Selected Substances SUBSTANCE* • Gastric juice (found in the stomach) Lemon juice pH VALUE 1.2–3.0 2.3 Vinegar 3.0 Carbonated soft drink 3.0–3.5 Orange juice • Vaginal fluid 3.5 3.5–4.5 Tomato juice 4.2 Coffee 5.0 • Urine 4.6–8.0 • Saliva 6.35–6.85 Milk 6.8 Distilled (pure) water 7.0 • Blood 7.35–7.45 • Semen (fluid containing sperm) 7.20–7.60 • Cerebrospinal fluid (fluid associated with nervous system) 7.4 • Pancreatic juice (digestive juice of the pancreas) 7.1–8.2 • Bile (liver secretion that aids fat digestion) 7.6–8.6 Milk of magnesia 10.5 Lye (sodium hydroxide) 14.0 *Bullets (•) denote substances in the human body pH of blood falls below 7.35, a condition called acidosis occurs, and if the pH rises above 7.45, it results in a condition called alkalosis; both conditions can seriously compromise homeostasis Saliva is slightly acidic, and semen is slightly basic Because the kidneys help remove excess acid from the body, urine can be quite acidic Even though strong acids and bases are continually taken into and formed by the body, the pH of fluids inside and outside cells remains almost constant One important reason is the presence of buffer systems, which function to convert strong acids or bases into weak acids or bases Strong acids (or bases) ionize easily and contribute many Hϩ (or OHϪ) to a solution Therefore, they can change pH drastically, which can disrupt the body’s metabolism Weak acids (or bases) not ionize as much and contribute fewer Hϩ (or OHϪ) Hence, they have less effect on the pH The chemical compounds that can convert strong acids or bases into weak ones are called buffers They so by removing or adding protons (Hϩ) One important buffer system in the body is the carbonic acid–bicarbonate buffer system Carbonic acid (H2CO3) can act as a weak acid, and the bicarbonate ion (HCO3Ϫ) can act as a weak base Hence, this buffer system can compensate for either an excess or a shortage of Hϩ For example, if there is an excess of Hϩ (an acidic condition), HCO3Ϫ can function as a weak base and remove the excess Hϩ, as follows: Hϩ Hydrogen ion ϩ HCO3Ϫ H2CO3 Bicarbonate ion (weak base) Carbonic acid JWCL316_c02_029-062.qxd 44 10/11/10 1:20 PM Page 44 CHAPTER • THE CHEMICAL LEVEL OF ORGANIZATION If there is a shortage of Hϩ (an alkaline condition), by contrast, H2CO3 can function as a weak acid and provide needed Hϩ as follows: H2CO3 Hϩ Carbonic acid (weak acid) Hydrogen ion HCO3Ϫ ϩ Bicarbonate ion Chapter 27 describes buffers and their roles in maintaining acid–base balance in more detail atoms, yielding a hydrocarbon Also attached to the carbon skeleton are distinctive functional groups, other atoms or molecules bound to the hydrocarbon skeleton Each type of functional group has a specific arrangement of atoms that confers characteristic chemical properties on the organic molecule attached to it Table 2.5 lists the most common functional groups of organic molecules and describes some of their properties Because organic molecules often are big, there are shorthand methods for representing CHECKPOINT 12 How inorganic compounds differ from organic compounds? 13 Describe two ways to express the concentration of a solution 14 What functions does water perform in the body? 15 How bicarbonate ions prevent buildup of excess Hϩ? 2.5 ORGANIC COMPOUNDS TABLE 2.5 Major Functional Groups of Organic Molecules NAME AND STRUCTURAL FORMULA* Hydroxyl R O H Alcohols contain an OOH group, which is polar and hydrophilic due to its electronegative O atom Molecules with many OOH groups dissolve easily in water Sulfhydryl R S H Thiols have an OSH group, which is polar and hydrophilic due to its electronegative S atom Certain amino acids (for example, cysteine) contain OSH groups, which help stabilize the shape of proteins Carbonyl Ketones contain a carbonyl group within the carbon skeleton The carbonyl group is polar and hydrophilic due to its electronegative O atom OBJECTIVES • Describe the functional groups of organic molecules • Identify the building blocks and functions of carbohydrates, lipids, and proteins • Describe the structure and functions of deoxyribonucleic acid (DNA), ribonucleic acid (RNA), and adenosine triphosphate (ATP) Many organic molecules are relatively large and have unique characteristics that allow them to carry out complex functions Important categories of organic compounds include carbohydrates, lipids, proteins, nucleic acids, and adenosine triphosphate (ATP) Carbon and Its Functional Groups Carbon has several properties that make it particularly useful to living organisms For one thing, it can form bonds with one to thousands of other carbon atoms to produce large molecules that can have many different shapes Due to this property of carbon, the body can build many different organic compounds, each of which has a unique structure and function Moreover, the large size of most carbon-containing molecules and the fact that some not dissolve easily in water make them useful materials for building body structures Organic compounds are usually held together by covalent bonds Carbon has four electrons in its outermost (valence) shell It can bond covalently with a variety of atoms, including other carbon atoms, to form rings and straight or branched chains Other elements that most often bond with carbon in organic compounds are hydrogen, oxygen, and nitrogen Sulfur and phosphorus are also present in organic compounds The other elements listed in Table 2.1 are present in a smaller number of organic compounds The chain of carbon atoms in an organic molecule is called the carbon skeleton Many of the carbons are bonded to hydrogen OCCURRENCE AND SIGNIFICANCE O R or R C R Aldehydes have a carbonyl group at the end of the carbon skeleton O C H Carboxyl O R or R C Carboxylic acids contain a carboxyl group at the end of the carbon skeleton All amino acids have a OCOOH group at one end The negatively charged form predominates at the pH of body cells and is hydrophilic OH O C OϪ Ester O R C O R Phosphate O R O P OϪ Amino H R N H or R ϩ N OϪ Esters predominate in dietary fats and oils and also occur in our body as triglycerides Aspirin is an ester of salicylic acid, a pain-relieving molecule found in the bark of the willow tree Phosphates contain a phosphate group (OPO42Ϫ), which is very hydrophilic due to the dual negative charges An important example is adenosine triphosphate (ATP), which transfers chemical energy between organic molecules during chemical reactions Amines have an ONH2 group, which can act as a base and pick up a hydrogen ion, giving the amino group a positive charge At the pH of body fluids, most amino groups have a charge of 1ϩ All amino acids have an amino group at one end H H H *R ϭ variable group ...JWCL 316 _fm_i-xxxiv.qxd 17 /11 /2 010 21: 22 Page i Principles of ANATOMY & PHYSIOLOGY 13 th Edition Gerard J Tortora Bergen Community College Bryan Derrickson Valencia Community College John Wiley... JWCL 316 _fm_i-xxxiv.qxd 17 /11 /2 010 21: 23 Page iv N OT E S TO The challenges of learning anatomy and physiology can be complex and time-consuming This textbook and WileyPLUS for Anatomy and Physiology. .. Dermis 15 9 The Structural Basis of Skin Color 16 0 Tattooing and Body Piercing 16 1 5.2 Accessory Structures of the Skin 16 1 Hair 16 1 Skin Glands 16 4 Nails 16 5 5.3 Types of Skin 16 7 5.4 Functions of